Doesn't work. Once you put it onto the battlefield as a land, the game sees an instant in play and derps out.

Could do it as a land with evoke?

If you want split cards like this, one could tweak the rules so permanent/spell split cards in play are the permanent half only. I think it would still be too confusing, but it seems like a plausible tweak to the rules, an extension of how they work on the stack.

If you just want this card, the simplest way is probably "2UU, discard this from your hand:". Although I think dual land/spell cards are really strong, because you don't get dead land draws later in the game, it might be better to make it a situational counterspell?

Mmm... even with the rule complication this is definitely strong. Not overpowered, per se, but it sure does shore up some holes in the standard counterspell deck.

Also, evoke or discard probably automatically increases the "casting cost", since that would make this card very close to being strictly better than Last Word.

As an activated ability, it can't be countered by normal spells. Only cards like Stifle can interfere. As an ability, it should be expensive and only soft counter.

For what it's worth, this card is almost identical to Denying Channel, the card originally submitted by Taigo Chan when he won the Magic Invitational. R&D tried playing with it for a while and decided it was too strong, so they asked him for another design. We wound up "merely" getting Snapcaster Mage instead. See http://www.wizards.com/magic/magazine/article.aspx?x=mtg/daily/arcana/826 .

Granted, this isn't uncounterable and it etb tapped as a land, but I still think that this is probably going to be a huge boon to slow, grindy control decks. It also doesn't lead to particularly many interesting choices: if you have other lands, you always hold it back; if you're mana hosed, you play it as a land. I'd much rather see the spell half of this be something that was relevant at the same point in the game that the land would help; perhaps something like, "U: Counter target creature spell unless its controller pays 1."

Oh, also the rules don't support split cards that are half-permanent, half-instant. But there are ways to work around this, so I wouldn't worry about it too much.

Or, come to think of it, it could be "2UU. Counter target spell or search your library for an island card and put it onto the battlefield tapped."

That would solve the templating problem even more simply, but sort of suggests it would be too good, since blue doesn't normally get that.

I like awall's suggestion.